IAAOJ, Scientific Science, 2014, 2(2), 10-25 THE EFFECTS OF 23.10.2011 VAN EARTHQUAKE ON NEAR-FIELD AND DAMAGED ON STRUCTURES Ercan Işık1 1 Bitlis Eren University, Department of Civil Engineering, Bitlis, Turkey e-mail: [email protected] ABSTRACT A destructive earthquake happened at 13:41 in 23.10.2011 in Van of which Mw: 7.2. The earthquake has been replaced between significant earthquakes in the earthquake history of Turkey by causing more than 600 deaths, over 2000 injured people, leaving thousands of people homeless and more than one billion dollars of economic loss. The earthquake has been felt in some settlements, especially in Lake Van Basin where earthquake has always been neglected. The highest peak acceleration values recorded at Bitlis-Centre Station after Van-Muradiye Station. Maximum structural losses observed in Bitlis after Van and Erciş District. The province of Bitlis settles in Lake Van Basin in the East Anatolian Region of Turkey. Bitlis is about 100km away from the epicentre of the earthquake. The first damage assessment of constructions after earthquake and its evaluation have importance in order to prevent loss of life and property in coming earthquakes. In this study the effects of earthquake on constructions in Bitlis have been observed and evaluated. The goal of this paper is to introduce major reasons for structural damages on the near field of 23.10.2011 Van earthquake at neighbouring province Bitlis. The damages have been observed that they overlap with typical earthquake damages. It has been observed that the negative features of constructions have caused an increase in damage amount. Almost no damages in constructions built according to Turkish Earthquake Code have been observed. And this has proved that codes are enough but buildings have not been constructed according to these regulations. Keywords: Van earthquake, Bitlis, masonry, reinforced concrete, structural damages, near-field, 23 EKİM 2011 VAN DEPREMİNİN YAKIN ALAN ETKİSİ VE YAPISAL HASARLAR ÖZET 23.10.2011’de yerel saat 13:41’de Mw=7.2 büyüklüğünde Van merkezli şiddetli bir deprem meydana gelmiştir. Bu deprem 600’den fazla kişinin ölümüne, 2000’in üzerinde kişinin yaralanmasın, binlerce kişinin evsiz kalmasına ve bir milyar dolardan fazla ekonomik kayıplara neden olarak Türkiye’deki önemli tarihsel depremler arasında yerini almıştır. Deprem, depremsellik öğesi ihmal edilen Vangölü Havzasında bulunan yerleşim birimlerinde hissedilmiştir. En büyük ivme değeri Van-Muradiye İstasyonundan sonra Bitlis-Merkez istasyonunda kaydedilmiştir. Van ve Erçiş dışında en büyük yapısal hasarlar Bitlis ve ilçelerinde meydana gelmiştir. Bitlis il merkezi deprem merkez üssüne yaklaşık olarak 100km uzaklıktadır. Deprem sonrasında yapılarda meydana gelen hasarların ilk tespiti ve değerlendirilmesi daha sonraki olası depremlerde oluşabilecek can ve kayıplarının artmaması için önem arzetmektedir. Bu çalışmada depremin Bitlis ilindeki yapılara etkileri gözlemlenmiş ve değerlendirilmiştir. Çalışmanın esas hedefi merkez üssü Van olan depremin yakın alanda komşu olan Bitlis ilindeki yapısal hasarları belirtmektir. Gözlemlenen hasarların tipik deprem hasarları ile birebir örtüştüğü gözlemlenmiştir. Yapıların olumsuz özellikleri, hasar miktarının artmasında önemli bir rolü olmuştur. Depreme dayanıklı yapı tasarım yönetmeliklerine uygun inşa edilen yapılarda neredeyse hiç hasara rastlanmamıştır. Bu da yapı tasarım yönetmeliklerinin yeterli olduğu ancak yapıların yönetmeliklere uygun inşa edilmediği gerçeğinin bir kez daha ortaya koymuştur. Anahtar Kelimeler: Van depremi, Bitlis, yığma yapı, betonarme, yapısal hasar, yakın alan 1. Inroduction In general terms, the risk can be defined as the combination of probability of occurrence and the consequence of a specified hazardous event. Otherwise, the value of risk depends on the severity of hazard and the vulnerability of the elements which will be affected by the hazardous event (Kundak, 2006). Earthquake damages will increase according to vulnerability of urban and rural building stocks. The size of earthquakes and Işık the negative structural features will be caused an increase in damage amount. Knowing the properties of buildings that have been negatively influenced to the seismic behaviour of buildings under earthquakes will be put forward to ensure more serious approaches to reduce the level of damage risk after earthquakes. The first damage assessment of buildings after earthquake and its evaluation have importance in order to decide to repair buildings and reinforcement or destruction of buildings according to the degree of damage. The possibility of occurring damage according to the size of earthquake is greater on buildings that have not been constructed according to earthquake codes. By the way there can be damages in buildings constructed according to earthquake codes after severe earthquake. Therefore, the determination of damage and doing the necessary strengthening continuation of this is one of the important topic of civil and earthquake engineering (Celep, 2004). The province of Bitlis settles in Lake Van Basin in the East Anatolian Region of Turkey which is considered to be one of the important provinces of that strategic corridor of Turkey. Bitlis is a town in and the capital of Bitlis Province which was 70,000 (including the surrounding villages) as of 2,000. The town is located at an elevation of 1,400 metres, 15 km from Lake Van, in the steep-sided valley of the Bitlis River, a tributary of the Tigris River. A popular folk etymology explanation, without any historical basis, is that it is derived from "Batlis", the name of a general said to have built Bitlis castle by the order of Alexander the Great (Armenian Soviet Encyclopaedia, 1976). Lake Van basin is located in Eastern Turkey that has suffered very severe tectonic deformation (Horasan et al 2007; Toker et al 2007). Destructive earthquakes that will be occurred in Lake Van Basin will be effect Bitlis and its districts which were also in this basin (Işık, 2010). In this context 23.11.2011 Van earthquake was felt strongly in Bitlis and its towns. In this study the effects of this earthquake on constructions in Bitlis have been observed and evaluated. This paper gives information about the characteristics of the site and soil conditions for Bitlis. Furthermore, it also gives information about tectonic settings and seismicity of Lake Van Basin especially Bitlis. The damages to reinforced-concrete (RC) and masonry structures after earthquake are observed, evaluated and recommendations made. The distance from the study area to the epicentre of Van earthquake is given in Fig.1. Fig.1. The distance from study to the epicentre of Van earthquake A destructive earthquake happened at 13:41 in 23.10.2011 in Van of which Mw: 7.2. The earthquake has been felt in some settlements, especially in Lake Van Basin where earthquake has always been neglected. The earthquake epicentre was located directly between Erciş district and Van City. Bitlis is about 100km away from the epicentre of the earthquake. Adilcevaz District is about 60km away from earthquake epicentre. The maximum structural losses observed in Van and Erciş District. Erciş district was the most heavily damaged area in this earthquake. Maximum structural losses observed in Bitlis after Van and Erciş District (Fig. 2.) IAAOJ, Scientific Science, 2014, 2(2), 10-25 Fig.2. Instrumental intensities associated with the main shock (Koeri, 2011) Turkish National Strong Ground Network operated by AFAD recorded the strong ground motion data for calculating the peak acceleration values for 23 October Van earthquake. Bitlis-Centre Station is 116 km away from epicentre of earthquake. The peak acceleration values recorded at Bitlis-Centre Station were 89.66, 102.24 and 35.51 cm/s2 in north–south, east–west and vertical direction, respectively. The peak acceleration values for 23 October Van Earthquake is given in Table 1. Table 1.The peak acceleration values for 23 October Van Earthquake (AFAD, 2011). STATION Accelerometer Values (gal) Type of Distance Share Wave Accelerometer No CITY TOWN NS EW UD Repi (km) Velocity Vs30(m/sn) 1 Van Muradiye SMACH 178.5 168.5 75.5 42 293 2 Muş Malazgirt SMACH 44.5 56.0 25.May 95 311 3 Bitlis Centre CMG-5TD 89.66 102.24 35.51 116 Alluvial 4 Ağrı Centre CMG-5TD 18.45 15.08 7.21 121 295 5 Siirt Centre CMG-5TD 9.90 9.16 7.04 158 Alluvial 2. Local Geology The local geological soil conditions have been affected and changed the characteristics of seismic activity. It is a known fact that this may cause damages cause damage on the existing structures that have been built on these grounds (Borcherdt, 1990). Lake Van Basin which contains Bitlis, has been located at that known as Bitlis Thrust Zone in geological terminology that was a collapsed tectonic basin which have been relatively to Eastern Taurus (Ozkaymak et al, 2003). Orogenic movements have occurred in the field until third phase of Miocene. Volcanic events have been caused to form many faults, depressions and large lakes in this period (Facenna et al, 2006; Köse, 2004). The structure and metamorphism of an area of 84 km2 lying on the Taurus Mountains of South-East Turkey was studied by researchers. The country around the city of Bitlis was mapped on 1/10.000 scale. The stratigraphical relations of the metamorphic rock units are quite obscure. Two major rock units mainly composed of unfossiliferous metamorphic rocks are distinguished on the basis of structural and petrographic evidences. Three deformation phases accompanied